In order for a computer or other microprocessor-based system to be in an operational state capable of executing multiple application programs (i.e., those programs that give the system specific functionality), the system must be under the supervisory control of operating system (OS) software. This operational state involves particular code and data being stored in memory that enable the OS to maintain supervisory control over how the system resources are allocated to the various application processes. The usual means by which the operational state is attained is through a boot sequence, in which the processor (CPU) first begins executing (e.g., upon powering up from a powered down condition) at a specific location in a non-volatile read-only memory (ROM). That is, the program counter of the CPU (or instruction pointer in Intel ×86 architectures) is initially loaded with the starting address of software in the ROM, usually referred to as the BIOS (basic input/output system) because of other functions performed by the software. The BIOS code contained in the ROM defines the basic steps taken by the system when it starts, including hardware detection and initialization and loading of the operating system by a bootstrap loader. Execution of the bootstrap loader causes the boot record of the storage medium containing the operating system software (e.g., a hard disk, floppy, or CD-ROM) to be read into system memory, which is usually volatile dynamic random access memory (DRAM). The boot record contains a boot program which is then executed to begin the process of loading the operating system into memory from the storage medium.
The process of booting the system is time-consuming because the operating system must perform certain computations in order to configure itself to the particular system, including hardware detection/initialization and the building of various data structures to be used in the management of system resources such as memory and processor time. In certain situations, it would be advantageous for a system to be able to transition quickly to a booted operational state without going through a lengthy boot process. It is toward that general objective that the present invention is primarily directed.